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Interacting Winds: Theory Overview Stan Owocki Bartol Research Institute University of Delaware with thanks for web slides from: D. Folini, K. Gayley, S. Lepine, M. MacLow, J. Pittard, I. Stevens, P. Tuthill, R. Walder
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July 10, 2000 2 Overview Hot-stars have massive, high-speed winds. These interact: Internally Large-scale, e.g. CIRs Small-scale, e.g., instability-generated turbulence In high-mass binaries, e.g. WR-O With environs: Previous epoch outflow, e.g. slow RSG wind ISM SNe High-speed shocks, often unstable.
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July 10, 2000 3 HD64760 Monitored during IUE “Mega” Campaign ¥Monitoring campaigns of P-Cygni lines formed in hot-star winds also often show modulation at periods comparable to the stellar rotation period. ¥These may stem from large-scale surface structure that induces spiral wind variation analogous to solar Corotating Interaction Regions. Radiation hydrodynamics simulation of CIRs in a hot-star wind Rotational Modulation of Hot-Star Winds
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July 10, 2000 4 Hot-star winds intrinsically unstable at small-scales < L sob v th /(dv/dr) Growth rate g /v th v /L # e-folds v/v th In 1D simulations, leads to formation of multiple shocks In multi-D, expect supersonic “compressive turbulence” Line-Driven Instability in Wind Acceleration Region Velocity Density t=430 ksec
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July 10, 2000 5 WR Wind Blobs Infer acceleration over extended scale: R * ~ 20-50 R O g rad ~ L * /4 r 2 c Requires radially increasing effective opacity ~ /m Possible from desaturation of optically thick blobs Yields ~ ~ r 2 g rad ~ constant! Lepine & Moffat 1999
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July 10, 2000 6 Colliding Wind Binaries Close binaries: X-ray attenuation Radiative forces Inhibition Braking Interface instabilities Wide binaries: Cometary or Spiral structure Radio Emission Dust formation
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July 10, 2000 7 Colliding Wind Momentum Balance Wind-wind balanceWind-radiation balance WR wind O-star radiation Symmetric or widely separated binaries Asymmetric (e.g.WR+O) close binaries
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July 10, 2000 8 Sudden Radiative Braking Diagnostic potential for line-driving opacity, e.g. in V444 Cyg Scaling analyses suggests broad importance in close to moderately separated WR+O systems Scaled Separation Scaled Momentum Ratio
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July 10, 2000 9 Dust Spiral in WR 104 Tuthill et al. 1999 IR image from Keck How does dust form?
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July 10, 2000 10 Wind-Blown Bubbles in ISM Some key scalings: WR wind bubble NGC 2359 d pc =V 1000 ø _ Mø m ¥ 4º 3 Ω(Vø m ) 3 ø m =100 s _ M °6 V 3 1000 n 1 yrs M= 4º 3 Ωr 3 º0:1M Ø n 1 r 3 pc r = √ _ M °6 ø 5 n 1 ! 1=3
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July 10, 2000 11 Formation of Prolate Nebulae Frank et al. 1998: Prolate fast wind into spherical medium -limit Langer et al. 1999: Fast spherical wind into slow, dense equatorial flow Gravity darkening
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July 10, 2000 12 Rayleigh-Taylor (heavy over light ) Vishniac & Thin-Shell (gas-ram) (ram-ram) Shock Interface Instabilities Kelvin-Helmholtz (shear) Cooling Overstabilty ga For summary, see J. Pittard Ph.D. thesis
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July 10, 2000 13 2D Planar Simulation of Interaction Layer Walder & Folini 1998,1999 Density Isothermal case: Thin-shell instability Radiative cooling case: Cooling overstability
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July 10, 2000 14 Questions Internal interactions What induces large-scale DAC structure? NRP? B-fields? What is lateral scale of instability structure? What is origin of WR blobs? Instability? Pulsation? What causes extended blob acceleration, >>1 Wind-wind collisions What reduces and softens X-ray emission? Absorption? Conduction? Instability mixing? Braking? Does Radiative Braking Occur? Even in clumped flows? How does dust spiral form? Wind-environs What determines nebula shape? e.g., in Car: What causes the axisymmetry? Magnetic fields? Rotation? Radiation? -limit vs. gravity darkening
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July 10, 2000 15 Radiative Shocks Hot Gas Cools by Line-Emission In 1D ideally develops characteristic layers µ∂ 4 N cool =7£10 17 V 100km=s cm 2
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July 10, 2000 16 Reduction of X-ray emission Instantaneous wind acceleration 3x10 34 erg/s 8x10 32 erg/s Radiative wind acceleration 3D simulations of V444 Cygni (J. Pittard, Ph. Thesis, 1999):
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